"This sample is impure, containing a small amount of calcite.
Despite this contaminant, the sample is spectrally featureless
throughout the range. The calcite probably only serves to slightly raise
its overall reflectivity."

Comment: Intensities do not match JCPDS data well. Optically, a large proportion of a
colorless phase with poor cleavage and high birefringence - presumably the wurtzite.
In the powder used for the X-ray data, the colorless phase is much coarser than the
opaque(s). Will regrind and make another pattern.